This invention relates to an improved dual mode antenna. With the advance in the microelectronic circuitry such as large-scale integrated circuits or LSI circuits, it has been possible to build a radio receiver of a very small dimension, even smaller than a regular cigarette package for use as a radio pager worn or clipped onto a person's pocket.
A popular commercial pager of such a size includes a receiving antenna formed of a conducting U-shaped member having substantially parallel elongated arms which form sides of the housing of the receiver. Normally, the radio is clipped on a pocket or worn on a belt of a person, and the U-shaped antenna acts as an inductive loop antenna to detect the H field of the electromagnetic wave caused by the transmitted signal. For a more detailed description of such an antenna, one may refer to the U.S. Pat. No. 3,736,591 to Larry W. Rennels and William J. Wilson, and assigned to Motorola, Inc., the assignee of the present application. The U-shaped antenna is compact and has been found rather efficient as a loop antenna.
It has been found, however, that when the loop antenna is held away from a body it becomes inefficient. If the pager is only a one-way pager, that is, a radio receiver only, then the loop antenna is satisfactory in that the reception of the signal normally takes place as the person wears the radio on his bent or clipped onto his pocket.
However, there are needs for two-way miniaturized radios, such as talk-back pagers, designed to receive and transmit radio signals. The aforementioned loop antenna is satisfactory when the radio is worn on the person as mentioned before. But it has been found that when the radio is held away from the body of the person using it, the loop antenna becomes inefficient.
Dipole antenna of the collapsible type is known. Such a dipole antenna is described in the U.S. Pat. No. 4,121,218 to James Stuart Irwin and Francis Robert Steel, and assigned to Motorola, Inc., the assignee of the present invention. While the dipole antenna is highly satisfactory for use with portable radio, it is not adapted for use with a two-way miniature radio or talk-back pager of the type worn on the body of person.